Telephone system



Jan. 13, 1931. c. D. KOECHLING TELEPHONE SYS TEM Filed March 13, 1929 6 Sheets-Sheet. 1

//v VENTOR L2 L7. KOEDHL/NB Jan. 13, 1931. c. D. KOYECHLING 1,788,528

TELElHONE SYSTEM Fil ed March 15. 1929 e Sheets- Sheet 2 ATTORNEY 1 Jan. 13, 1 931. c KQECHLING 1,788,528

TELEPHONE SYSTEM Filed March 13, 1929 6 Sheets-Sheet 5 Jan. 13, 1931. c, KOECHLING 1,788,528

TELEPHONE SYSTEM Filed March 13, 1929 6 Sheets-Sheet. 4

Jan. 13, 1931. c. D. KOECHLING TELEPHONE SYSTEM Filed March 13, 1923 e Sheets-Sheet, 5

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. //v VEN TOR U. Q KUEGHL/A/z;

Jag. 1 3, 1931. c. D. KOECHLING 88,528

TELEPHONE SYSTEM Filed March 13, 1929 6 Sheets-Sheet 6 INVENTOH 0. L7; KQEEHL/NG A 7' TURNEY 7 shows two additional trunk lines leading to a Patented Jan. 13,1931" I osrrrzo STATES YORK PATE

CHARLES E. Koncnrrns, oEBRooKLYnnEw YORK, assreitoa To B LL 'TEIiErHoNE LABORATORIES, INCORPORATED, or NEW YORK, 1v. r. ,'aoonro1tATIoi roE NEW TELEPHONE sYsTEM Application filed March 13, 1929. seriaiir'o. 345,55G.

This inventionr'elates to telephone systemsa central oilice and under normal conditions and particularly to smallcapacity intercom municating service.

In the. present system, relays are used to connect local linesto trunks under direct se lective control and through links to' other local lines through selective dial control.

A feature of this invention is an arrangesystems having central oflice ment whereby certain stations having no ac? cess to the outgolng trunk lines are connected through switching means at other stations which do have access to trunk lines and by means of Which and under the supervision of the subscriber at such other substation may be temporarily given access to a trunk. This arrangement comprises a key set providing means operable by the subscriber thereat for ringing the restricted service subscriber,

formonitoring on the restricted service subscribers line and for transferring the restricted service subscribers line to an unrestricted service line.

Another feature is an arrangement whereby with a pluralityof stations on a line, each provided with means for establishing and controlling a connection to a trunk such con trol is exclusively appropriatedby thestation' first to exercise it.

Figs. 1 to 6, when placed as indicated in 7, diagrammatically llustrate thefvarr ous circuits comprising a dial P. B. X. embodying the features of the present invention. Fig. 1 shows three substation lines and one trunk line leading to a central ofiice,,Fig.2

central office, Fig. 3 shows a linecircuitffor each of the substation lines of Fig. 1 andthe. connecting relays for a first link circuit, Fig. shows the connecting r'elaysfor two additional link circuits, Fig. 5 shows the opera? ingrelays for the link circuit of Fig. 3, and

Fig. 6 shows various auxiliary circuits, such exchange. The two conductors land 2 lead from an ordinary subscribers line circuitlat would have ground and battery thereon through the winding of a line relay at the cen tral oilice.

We will assume that a connection has been made to such line at the central oificeand that ringing cur'rent'is being transmitted thereover from any well known source ofring'iiig current under machineconditions. This presupposes a ringing interval of approximately With relays 4 and 6 operated, ground is placed on each of conductors 7 8, 9 and 10. The ground on conductor 7 comes from the in"- ner right-hand armature and from contact of relay 4,through;the front contact and in ner righthand armature of relay 6, the lefthandarmature and back contact of relay 5. Ground on conductor 8 comesfrom the-outer left-hand armature and front contact of re lay ,6. Ground on condu ctorflflcomes {from the innerlett-hand armature and front coni) tact ofrelayfi and ground on conductor 10 comes from theouter right-hand armature and front contact of relay 4,

'ture'and front contact causes the operation of Conductors 7, 8,"9 and 10, may now be I tracedfdircctly to Fig.6 where it will'be seen that the round on cb'nductor'lO ener izes m I z: I y 11 and the ground on conductor 7 1s by another ground supplied over the r 12. Thisground' maintains relay 6 ener- Zed when relay l becomes deenergized dura silent interval.

round on conductor 9 now passes through the 1 right-hand armature and back con t L 13"through resistance 14, right-' winding of relay 15, back contact and inner left-hand armature of relay 13, resist? a ca 16, to battery and ground. Another circuit is establishedtrom the groundon conductor 9 throu gh the inner right-hand arm:

thand armature and back contact of reture and back contact of relay'18 to one terminal of condenser17, the other terminal of which is connected through resistance 18,

in the slow operation of relay 15 whereby it is approximately one-half second before re lay 15' becomes energized. At-this tune a circuit established from ground, the front contact and armature of relay 15, winding of relay 13 to battery and ground. Relay 13 immediately energizes and through its inner right and left-hand armatures reverses-the current supply to relay 15 and condenser l7,

whereby relay 15 which is polarized becomes deenergized, through the reversal of current initsright-hand winding and the discharge of the condenser in its left-hand winding. The release of relay 15 opens the circuit of relay 13 causing another reversal of current in the right-hand winding of relay 15 and the a Y groundzis removed fromconductor 19 where condenser 17. a a

, Thus, as long asground is ma ntained on conductor 9, relays'13 and 15 will act and react "so that ground is periodicallyconnected to conductor 19 from the outer left-hand armature and front contact of relay 18. Re-

lays 13 and 15 and the connecting resistances and condenser 17 are so adjusted in their values that ground is periodically placed on conductor 19 for one-half second and'take'n offfor one-half second, thus requiring a full second for a complete cycle of operations of relays 13 and 15. a

, In, order to more clearly explain the following automatic action of the ringing and timing circuit, we shall'spealr of a series of perrods as measured by the operation of relay 13 lhus, the first period will be a one-half second -operationof relay 13-, the second period will be a one-half second releaseof relay 13, the third period a one-half second operation of relay 13, etc. A f V At the beginning of the first period ground will be connected from conductor'19,through the alternate contacts of the left-handarmature of relay 20, winding of relay 20, resistance 21, tobattery and ground- Relay 20 will operate in this circuit and Will lock through its left-hand armature and alternate contact to the ground on conductor 9. The ground on conductor 19 will also be connected through the inner left-hand armature and back contact of relay 22, to one terminal of relay 22 so that this relay is now short-circuited and prevented from operating. I

At the beginning of the second period,

. ground is removed from conductor 19 where lay 20 becomes energized as before.

however, has no effect on either'relay 2 1 or 27. At the beginning of the sixth period, relay upon relay 22 becomes energized in a circuit from ground on conductor 9, the left-hand armature and alternate contact of relay 20,

Winding of'relay 22, resistance 23, to battery gized. e V

At the beginning of the third period,

and ground. Relay 2O ismaintained energround is again placed on conductor 19 whereupon relay 20 is short-circuited through ground on conductor'19 being BX-V -te1'1decl over the'inner left-hand armature and 7 front contact of relay 22 to one terminal of time a circuit is established from ground, the

right-hand armature andfront contact ofrelay 22, the back contact and right-hand armature of relay 20, the alternate contacts of the left-hand arinatureof relay 24:, resistance 25, l V

to battery and ground. Relay '24 becomes operated and locks to the ground on the con duct-or 9through its left-hand armature and alternate contact. Relay 27 is short-circuited through its left-hand armature and back contact. e

At the beginning of the. fourth period,

upon the circuit for relay 22 is opened and this relay becomes deenergized. At this time, due to themovement of the right-hand armature of relay 22 the short circuit about the winding of relay 27 is removed and this relay now becomes energized in a circuit from.

ground on conductor 9, the left-hand armature and alternate contact ofrelay 24, wind ing of relay 27 resistance 26, to battery and ground. I l

' At the beginning of the fifth period, ground is again placed on conductor 19 whereupon re- This,

22 becomes energized as before but this again has no effect on either relay 2 1 or .27.

At the beginning of the seventh period, ground is again placed on conductor 19 whereupon relay 20 becomes .deenergized as before but now since relay 22 is energized acircuit is established from' ground, the right-hand armature and front contact of relay 22, the back contact and right-hand armature of relay 20, the left-hand armature and front contact of relay 27,1esulting in the' short circuit of relay'24, whereby this relay becomes deener-w gized, At this time also a circuit is estab-.v lished from ground. the right-hand armature and back contact of relay2t, the front contact and right-hand armature of relay 27, the a1 ternate contacts of the left-hand armature of relay 28, resistance 29, to battery and ground resulting in the energization of relay 28.- Re]- lay 28 now locks through its left-hand armatureand normal contact to the ground on conductor 9, andrelay 31 is ,short-circuitedthrough this ground and the ground on its left-handarmature leading to its other ter ininal. The energizationof relay 28 results in the cnergization of relay 32 so that relay 32 1s first energized at the beginning o1 the seventh period.

At the beginning of the, eighth period,

ground isremoved from conductor 19 where 1 by relay 221s deenergized as before and relay 2'7 becomes deenergized as theresult thereof. A circuit is now establishedfrom ground on conductor 9, through the left-hand armature and alternate contact of relay28, winding of relay 31, resistance 30, to battery and ground resulting in the operation of relay 31'. 28 islnaintalned energized.

At the beginning of the ninth periogd ground 18 again placedon conductor 19 where 7 Relay ,1 by relay 20 becomes operated as before At this time a circuit is established from ground, r1ght-hand armature and back contact of .re-

lay 22, front contact and right-hand armature of relay 31, back contact and right-hand ar- :nature of relay 20,,alternate contacts of the left-hand armature of relay 24:, operation of relay 24 as before.

At the beginning of the tenth period,

to, cause the 1 relay 2' becomes operated thus opening theoriginal energizing circuit of relay 2% and resulting in the energization of relay 27,

At the beginning of the eleventh period, relay 20 becomes deenergized whereupon a circuit is established from grounrhthe righthand armatureand front contact of relay 22'.

the back contact and right-hand armature of relay 20, the left-hand armature and front contact of relay 27, to cause the short circuit of relay 2% which now becomes.deenergizedi With the deenergization of relay 24whilerelay 27 is still energized, a circuit is etablished from ground, the right-hand armature and back contact of relay. 2%, front contact and right-hand armatureof relayz2'l, the left- "-.and armature and front contact of relay 31 to cause the short circuit of relay 28 which now releases in turn releasing relay 32. Thus, relay 32 has been maintained energized over the seventh. eigl1th,-ninth and tenth periods,- a total periodof two seconds.

At the beginning of the twelfth period. ground 13 removed from conductor 19 whereupon relay 22 is released, resulting in the release of relay 2?. Through the release of relay 27, relay 31 becomes dee'nergized and at this timeall therelays, in this group are at normal.

At the beginning of the thirtenth period,v this entire cycle of operations begins over again, Thus, it will be seen that out of twelve periods, relay 3'2-is energized for a total of tour periods and deenergized for a total of eight periods. meaning that the relay 32 operates periodically to connect the source of ringing current 33th-rough its arinatures and front contacts'to-conductorsile andi35 for period of'two seconds; andto connect-ground and battery through its back contacts andar matures .to these. conductors for a period of four seconds.

.lltfwill be seen that while relay 131 is periodicallyplacing ground on the conductor 19, for half-second periods that relay 22 is also periodically closing its left-hand outer contact for one-second periods, it has been seen that relay 11 is energized durlng the encigization of relay l. During its periods of encrgization an alarm 36 is operated from the source of current :83, throughthe closure oi" the right-hand armature and front con;

tact ofrelay 11. V I l Also during these periodsv ground con nected to conductor "37 through :the closure of the outer left-hand armature and front contact of relay 22 isfdisconnectedfrom pair of relays 38 and 39. :In the same manner the round on conductor 8 1s d1sc0nnected of explanation will now assume anew series of periods, in this case, each of one-second duration. v r

lit the beginning .of the first period, relay 22 will become energized and relay 11 will operate,

At the beginning of the second period, relay 22 will release but relay 11 will be maintainedoperated through the, two-second energizationwhich it receives under control of relay at;

At the beginning of. the third period, relay 22. will become. energized and at this time relay l1 willbecome deenergized. Upon the deenergization of relay 11 a circuit is established from ground. on conductor '8, through the outer left-hand armature and front conand inner left-hand armature of relay l1 alternate-contacts of the left-hand armature of relay 38, winding of relay B8, resistance 40, to battery and ground. Relay 38becomes;

energized in this circuit and locks to ground on conductorS through the outer left-hand armature and back contact of relay 11,, lefthand armature and alternate contact of revlay" Relay 89 is shortcircuited at this time through its own left-hand armature and back contact. r h

tact of relay 22, conductor 37, back con-tact At the beginning of the fourth period, re

lay 22 becomes deenergized and by removing I lay 39, resistance 41, to battery and ground.

At the beginning of the fifth period, re-.

lay 22 again operates, thus again placing ground on conductor 37 which results in the short-circuit of relay 38 and this relay there fore releasesr Through the release of relay 38, gound on the conductor 8 is connected through the outer left-hand armature and back contact of relay 11, right-hand armature and back contact of relay 38, front contact and right-hand armature of relay 39, alternate contacts of the left-hand armature of relay 42, resistance 43, to battery and ground. Relay 42 becomes energized in this circuit and through its right-hand armature places an additional ground on conductor 7.

At the beginning of the sixth period, relay 22 releases whereupon ground being removed from conductor 37 relay 39 is released. With both relays 38 and 39 released and relay 42 operated the short circuit about the winding of relay 12 is removed and this relay now operates. Although by its operation relay 12 removes ground from conductor 7, this conductor is maintained grounded through the right-hand armature and front contact of relay 42 as just described.

At the beginning of theseventhperiod, relay 11 again operates, resulting in the immediate deenergization of relays 42 and 12 whereby relay-s 12, 38 39 and 42 are returned to normal to thus prevent the possibility of removing ground from conductor 7. This con-.

dition will be maintained as long as relay 11 is periodically operated for periods of two seconds and released for periods of four seconds. If, however, before the beginning of the seventh period, relay 4 has be-' come permanently deenergized as by the abandonment of the connection from the centralotfice then the operation of relay 22 and the failure'of relay 11 to reoperate will result in the extension of ground from conductor 8 through the outer left-hand armature andfront contact of relay 22, conductor 37, back contact and inner left-hand armature of relay 11,'alternat-e contacts of the left-hand armature of relay 38, to the winding of relay 38 to cause lts operatlon. Upon this second operation of relay 38, ground supplied over conductor 8 through the outer left-hand armature and b ack contact of re lay 11, to the right-hand armature ofrelay 38, is opened at this point so that relay 42 becomes deenergized. Upon the deenergization of relay 42 while relay 12 is energized and relay 11 is deenergized, ground will. be;

messes ing current comes in over conductors 1 and 2 from the central ofiice even though this 'ringingcurrent is-periodically applied for periods of two seconds and disconected for periods of four seconds. Signal lamp 45 and multiples thereof together with associatedsignal lamps 46 and 47 for other incomin trunks, and alarm 36 and multiples thereof, are placed at strategic points about the premises wherein a P. B. X. of this nature is installed. Any one of the subscribers noting the lighted condition of lamp 45 and hearing the alarm 36 may answer the incoming call. a a

Let it be assumed that the subscriber at substation 48 answers the incoming call. In this case he will operate trunk key 49 which through a well known mechanical locking arrangement will be maintained operated until manually released. The subscriber at subs" ation 48 will then remove his receiver from its hook whereupon a circuit will be established from battery, trunk relay 50, contacts 51 and 52, of key 49, resistance 53, contacts 54 and 55 controlled by hook switch 56, back contact and armature of relay 200, winding of relay 201, winding of marginal relay 57, to ground. WVith resistance 53 included in this circuit, relays 50 and 201 will become energized but relay 57 will fail to operate. Before proceeding with the other operations which take place when the subscriberat substation 48 answers the call coming in over conductors 1 and 2, the function of relays 200 and 201 will be explained. Sub-j station 202 is an extension of substation 48. It is seen that when substation 48 sets up a trunk call that relay 201 is operated. If during this period the subscriber at substation 202 should press his trunk key 203 and then remove his receiver from its hook, a connection would be established from ground and battery, trunk relay204, conductor 205, contact-s 206 and 207 of trunk key 203, resistance 208, contacts 209'and 210 controlled by switchhook 211 and'thence to the back con- 7 tact of relay 201,, but since relay 201 is now energized, the circuit cannot be completed and therefore the subscriber at station 202 [cannot interfere with the trunk connection tacts of the outer left-hand armature and agresis'at have first established a trunk connection, then relay 200 would bev operated to prevent the subscriber at substation 48 from" interfering With such connection.

Going back now to the operationsincident to the removal of the receiver from the switchhook. at substation 418, it will be noted that upon the operation of relay a circuit is established from ground, front contact and right-hand armature of relay 50, winding of relay 58, normal contact and 'inner righthand armature of relay 58, inner right-hand armature and back contact of relay 5 to battery and ground. Relay '58 operates in this circuit and holds through the alternate con tacts of its inner right-hand armature, Winding of relay 5, to battery and ground. Relay 5 now becomes operated and removes ground from conductor 7. The trunk conductors 1 and 2 are now connected through the front contacts and'left-hand armaturesof relay 58 to the talking conductors leading to sub station 48 whereupon the well known tripping relay at the centralotfice is energized, ringing current is stopped, and the talking condition is established. Belay 4 becomes deenergized and since ground is now removed from all of conductors 7 8, 9 andlO the relays of the ringing and timing; circuit are restored tonormal and signal lamp 45becomes dark.

It will be noted here that should another subscriber now attempt to make connection to this central ofiice trunk, such connection will bepre-vented through the removal of the battery connection from the back contact and inner right-hand armature of relay 5.

- As an illustration we will assume that the subscriber at substation 59 removes his handset from its stand and operates trunk key 149 whereby relay 150 becomes energized. Due

to the fact that relay?) isenergized relay 158 cannot become energized. Therefore, a c ir= cu1t Wlll beestabhshed from ground, the confront contact of relay 150, conductor 16%, winding of relay 165 to battery and-ground.

Relay 165 attracts its 'armatures and cuts off: the connection of the subscribers line to line;

relay 166.. At the same time a circuit is established from ground, outerfleft-handarmature and front contact of relay 150, outer left-hand armature and back contact of relay 158, over the loop of the subsc ribers line,

the inner-left-hand armature and'back con tact or relay 1 58 the nnerleft-hand armature and front contact of relay 150,:conductor 167 which may be traced through Figs. .2, '3,

5 and 6 to the winding of relay 168 and thence to batteryand ground. Relay 168 becomes energized '1I1 this circuit and through its armatureand front contact causes the operation of relay 132. Relay 132 in tu'rn'places ground on conductor 9' thereby starting the ringing and tun ng circuit relays into operatlon. Relay 132 through lts lnner right-hand armature and front contact also energizes the tone relay=122 so that this relay now vibrates its armature and through induction between its left and right hand windings" acts as a source of tone from which tone'c'urrent flows from its left-hand winding, through condenser 123, the outer right-hand armature and front contactof relay 13, during its periods of energization; through the outer right-hand armature and front contact of relay 132, condenser 169 to conductorl'd'? whence it is connected to the subscribers stae tion 59. This constitutes a busytone which notifies the subscriber thereat that the trunk reached through the manipulation of key the relays of the P. B. is a two-conductor line andthat it is not provided with aset of a trunk keys or trunk connecting-relays such as those associated with substations 4 8, 59 and 202. Substations of this nature are provided in theP. B. X. *where' it is expected that little or no service through the trunks will be needed and where the distances from the relay banks to the substations are com paratively long. v In order to'provide service for these substations over the trunks, therefore; a switch ing arrangement is provided in association with another substation which maybe centrally' located and where there will always be someone to attend to the service. The line of substation 1,60 therefore'enters a switching arrangement shown to the right of the trunk keys of station. 59' and which actually located at substation 59 and may be manipu-' dition on the trunk. This is done by pressing key 60. It will be noted that ofthefive' keys. 49, 60, 61, 62, and 63at substation 4C8 ferent form from the others. This-isto in- .115v if at substation 48is to establish a holding condicate that key No; 60 is nonlocking and as soon as the finger is taken off it will restore. 4

to its normal condition. The; other keys, however, are mechanically arranged so that the depression of one will restore any other which has been previously operated and maintain the one in operated position.

TV hen in the present instance key 60 is dek 12o thatkeyNo'. 60 is shown insomewhat difi 45 y r traced from Fig. 5 tofFigfS hand armature and outer left-hand armature connects the winding of relay across the conductors 1 and 2.. Relayr65 is now energized bythe current supplied at the central oflice and upon operation closes a circuit for the energization of relay 66. Relay-66 upon energizing opens a. short circuit about the winding ofrelay 67 which is now serially included in the circuit leadin to substation 48. Relay 67 therefore becomes operated and through its right-hand armature completes a lockingcircuit for relay 64 so that this relaydoes not deenergize when key 60 is returned to normal. 7

- The subscriber .at substation lSnow operates local key 61.; This key has nocontacts and does not produce any direct circuit change, but its operation unlocks key 49 whichupon restoring opens the 'circuit of relay 50. Relay 50, inturn releasesrelay 58' so that substation 48v isnow disconnected from the trunk circuit. Upon the release of relay 58 relay 67 becomes deenergized resulting in turn in the deenergization of relay 64. Relay? 65, however, is maintained energized in a circuit from conductor 1, the lefthand armature and back contact of relay 67, winding of relay 65, the armature and front contact of relay 66 to conductor 2. This formsc a shunt across the conductors 1 and 2 whichwillho-ld the connection at the central office.

. Since the subscriber established from ground, back Contact and right-hand armature of relay 68 in the tone circuit in Fig. 6, conductor 69 which maybe through theIleft-hand winding of relay; the back contact and .leftehand armaturexof relay 71, the back contactand left-hand armatureot relay 7 2, conductor 7 8 to and through I the loop ofsubstation 48f, conductor'l't; in-' ner right-hand armature and back contact of relay 72, right-hand armature and back contact of relay 71, right-hand windingof relay 70. to battery and ground.- Relay 7O becomes energized int-his circuit;

A connection is now established from ground,the right-hand armature and contact of relay 70, the left-hand armature jet 78 of'relay 79, right-hand winding oi relay and back contact of relay 76, contacts 77 and 80 to battery and ground. 7 Relay 80 becomes energized in this circuit whereupon acircuit is established from ground, thewinding of relay 90, the righthand armatureiand back at substation a8now has lllS recelver oi'tt-he hook connect on 1s and thence contact of relay-91, conductor 92, inner. lefthand armature and front contact of relay 80, left-hand winding of relay 80 to battery whereby relay {BO-becomes locked in acircuit independent, of its right-hand windingzf Upon the energization of relay a, circuit is established from ground, left-hand armature and front conta-ct o'f relay 90, conductor 89, winding of relay .79 to batteryand ground. Relay'79i becomes energized inthis circuit and its armature is mechanically locked in operated position by means of latch 93 which is under control of relay 9%. Upon the energizat-ion of relay 7 9 the original energizing circuitofrelay 8O isv opened, but this relay is held in the locking circuit just described.

' Alsoupon the energization of relay 70, conductors 81, 82 and 83 leading respectively to theleft-hand windings of relays 84, 8-3 and 86 of the three link circuits are connected to ground. Therefore upon the energization ofrelay. 8O ground on conductor 81 connected through the lett hand winding of relay 8% is now extended'through the inner right-hand:

arm ature and front contact of relay '80,-conductor 87 ,back contact'and; armature otr'elay 88 to battery and ground.v Relay 84 becomes energized and establishes a circuit :fromjbatte ry and ground, right-handz winding of relay 8%, front contact and outer right-hand armature of relay 8; to groundon conductor 89, whereby relay 84 becomes locked in a circuit independent of its left-hand winding.

Upon the energization of relay 84 a connection is established from ground, theinner right-hand armature and frontcontact of relay 84, winding of relay 71 to battery and ground- Relay 71 cuts oit the win dings of the line relay 70. and extends the talking conduc tors Band 74: to conductors 95 and 96 respectively which now through the left-hand-a rmature and-front contacts of relay 84 are extended ;to-conductors 97 and 98 respectively and from thence through the leftwha nd wind ing to ground and the.right-handwindingto battery ofrelay 99so that relay 99 supplying current over theloop of substation 48 now becomes energized. Relay 99' establishes a connection from ground, armature and front contact of relay 99, windinguof relay 100m battery and'ground. Relay 100 becoming en'- ergized establishes a circuit from battery and ground, winding of relay 101, front contact and armature o1 relay 100, normal contact traversed by switch arm 102, normal contact of the left-hand armature "of relay 91. to

ground- Relay lOlbecomes energized in this circuit and through ts inner right-'hand ar- 1 mature establishes a circuit tor'the energization of relay 103., Thisrelay through its right-hand armature places ground on the, conductor 89, and throughits left hand armature causes the energization of relay 91, Re-- lay-r91 through its alternate contact and lefthandarmature now maintains relay'101 ener-.

normal. Relay being in seriesnwith th holding winding of relay 80, relayx80 now bec m deenergizedr t will no dat this point that shoe-1d anot e call no he originated whereby conductor 104 s g ou ded s before, that' such ground will now be. extended through the leftshand armature and back contact of re: lay 7 6, contacts 105 and 106; of relay 79, back contact and Outer left-hand armature ofrelay 8( left-hand armature and back contact of relay 107, c0ntaots108 and 109 of relay 110 to. the right-hand winding ofrelay 111. Res.

lay 111 it will benoted'controls the second link circuit so that upon: the energization of relay 8.4 hereinbefore described the starting circuit isadvanced. i

In this connection it will furthermore be noted that throughthe energization of relay 88, battery is removed from'conductor .87 so that. no one of theline finder relays'suoh as 8 Shown on a horizontal line'tothe right thereof may become energized. The link circuitis now-in a condition awaiting reception of d al pulses from the substation 48: n 30 7 Upon the energizationof relay 90 hereinbefore described and the subsequent energiza- ,tion ofrelay-103, whereby ground is placed on conductor 89, a circuit is established from such ground, through the normal contacts of the armature of relay'114, brush 111i and its normal contact, through the winding-of relay 119, to battery and ground. Relay 119 is known asthe dial tone relay and through its right-hand armature connects ground to: con: ductor 120 leadingihrough resistance 121, the back-contact armature and" rightvhand winding of relay 122 to battery: Since. this circuit includes "the back contactof the. relay which becomes energized therein, the relay will vibrate its armaturerapidl-y and through induction will transmit atone through its left-handwinding condenser 123 over con.- ductor 124, thence through the front contact of the right-hand armature of relay 119, condenser 125, through the rightehand winding of relay 99 to'battery. Thence by induction this tone will be transmitted to the 1 subs scribers station 48, notifying the subscriber that he may proceed withfthe dialing o e ation.

It has beenassumed that the subscriber at substation 48 wishes to communicate withlthe subscriber at substation 5.9. He will there: fore operate his dial to send three impulses each of which willhereconsist of a momen tary openingof the linewith the consequent momentary deenergization of relay 9,9. Upon the first deenergization'of this-relay a circuit is established between ground, armature and back contact of"re1ay,99, outer rightehand armatu e and trout eontacto r ay- 101., ight hand armature-and back contact of relay 11.2"; innermost right-hand armature and back contact of relay 113', windingof relay 114, wind ing of stepping magnet 115, to battery. and ground. Relay 11 4 becomes energized in this circuit and 0116.118 the circuit for dial tone rolityllS), whereby dial tone is-cut-off from the calling subsoribers line.

Also through the movement of its armae ture, relay 114 causes the energization of re lay126 which prepares a circuitfor the sub.- scquent energization of relay 113. The

ground for operatingthe stepping magnet 11.5; isalso extended through the armature and back contact of magnet 115, the lefthand armature and front contact of relay 1.01, the winding of relay 116, tobattery and ground. Relay 116 through its right-hand armature provides. a substitute ground for 'holdingrelay 100 operated, and through its rightehand armature provides a ground to supplement that from theback contacto-ii' relay 99, whereby" a ground is definitely maint ained on the Winding of stepping mag net until it has completely operated. This insures thatthe magnet-115 will take atoll step even though the momentary dee energizationof relay 99'is of such short duration that it would not ordinarily produce this result; 4

Upon the subsequent energization of relay 9.9. and when the magnetllfi has become fully energized, its circuit Willthen become opened and upon its release will drive brushes 102 and 117.0n to their first working contacts. Relay 114 tends to become deenergized at this time, but dueto itsslow releasing characteristics will'ho'ld itsarmature operated during .a full series of impulses. 11

In this manner the magnetllo is energized threetimes in succession that brush 117 comes to rest on the terminal connected to conductor-118.

Conductor 118 leads to relay in Fig. 3

117, conductor118, winding of relay 127 to 2 battery and ground and this relay now be: j 1

. comes operated.

For purposesof,illustration it will first-be assumed thatthe'line leading to substation 59 is busy. Inthiscase the cut-011" relay 128 i wines operated and a groundwillbe found on conductor 129. Therefore the'ground on conductor 129 will-be extended through the right-hand armature and front contact of relay 127i, conductor 130, armature and front,

contact-ofrelay 126, winding of relay 113 to battery andjground; xRelay llal responds and. locks through'its inner left-hand, armature toground on conductor 89.v This action takes place shortly :after the deenergiza'tion:

ofre'la 114] b vir-tueof the slow releasin y a 1 a:

tharacteristic of relay 126 Wh'ich holds its armature operated-tor an instant after-the link connector relay 127 has become oper atcd. o 4

. Relay 11.3in operating performs a number of functions. First, through its innermost right-hand 'arn'iature it opens the pulsing circuit so tl at the switch will be prevented from stepping should another digit be dialed. Secondly..relay 113'opens' the sieeve circuit froni'the back contact ofrelay-126 so that relay 112 is prevented from operatin Thirdly,' relay.113through its outermost right-hand armature and front contact places ground on conductor 131 which connects throughthe Winding of relay 132 to batteryand ground; Relay 132 through its left-hand armature places a ground on con ductor 9 Whichin turn energizes the ringing and timing relays in the manner herein-'- before; described. Through its inner rightco t hand armature relay 132' energizes the tone relay .122 so that: a tone isinow connected to conductor-124C. and thence :through the outer right hand armature ard frontcontact of relay 13 during its periods of energiz a tion, through the outermost right-hand armature and front cont-act of: relay 132,,condenser 133,- conduct or 134, front contact and middle right-hand armature of relay'113,

condenser 135, right-hand Winding or" 'relay 99 to-b'atter: ,Wh'encethrough induction the busy tone is periodically applied through the calling subscribers lineand the calling subscriber is thereby notified; that the called line is busy.

The circuit will remain .in this condition untilthe subscriber at substation 4C8 replaces the ground of the relay 112, whereupon both of these relays will become Q11GI'g1Z-OCl."R -E' lay 112 looks through its left hand'winding to-the ground on condurtor139 and by its righthand armature opensthe. pulsing cir cuit to prevent the switch'fronr-stepping.it another digit is dialed.- Through its left- T hand armature and: front contacts relay '112 extends the groundfon conductor 89 through theiniddle lowerarmature and back act of relay,13$,lthrough.the Winding of relay 13'? to battery and ground.

Relay 137 becomes operated, and through 'itsjinnerzlower armature places a ground on conductor 130 to operate the-cutoff rela-y line as busy.

128. Ground on conductor 12;) [marks this relay 137' through its inner upper armature and front Contact places a ground on nectedto conductors 138 and 139 and thence through the front contacts and left-hand arnia-turcs of relay 127 to conductors 1&2 and 143 respectively andthence through the front contactsand arina-tures of cut'ofi relay128, to the conductors'leading to substation 59.

- it will be notedthatsubstation 59 is shown in a difierent manner from' substat on 18. This is to illustrate the modern circuits used in connection with the handset. Thebell at the substation 59 will respondto the ringing current. now being transmitted theretofbut relay 141 ,not receiving'sufficient, current for its energizatioir will fail to operate. Relay 136 at this timev is: shunted through the I back contact of'relay 141 so that it does 'not' oper ate. 7 During the transmission of ringing current to the called. subscribers line,asmall amount is. shunted through conductor 139, through condenser 144, the backcontaot and middle right-hand armature or relay 113, condenser 135, through the righthand Windingot relay 99, Whence'by induction the calling subscriber at substation 48 is notified that substation59 is being. rung. WVhen the handset'atsubstation 59'is lifted from its sta-nd, the-contacts 145 are operated, thus putting thetransmitter' and receiver-in circuit and increasing thecurrent flowi'n relay 141 tothe point where this relay becomes operated; Theshunt around the Winding of relay 136 is nowreino ed' andthis maybelay becoines operated in a circuit from b attel-y, resistance146, winding "or relay 136,

front'contacts and left-hand armature of relay 112 to ground on conductor 89.

The operation ofrelay 136 opens-the'cir cuit of relay 1 37-jand thislatter" relay in rel'easing disconnects ringing current from the called line and removes the ground from conductor9l Relay 136also provides a substitute ground 'for the sleeve conductor and throiwh its inner armatures and front-con call coming in overthe central oficeiline rep' m "tacts extends-the talking circuit through -resented by conductors 1 and Without tion is established from battery and ground, 1 winding of relay150, contacts 151- and 152 of key 149,. resistance 153, contacts 154' and 155,- winding ofrelay, 157- to ground.- Belay150 Zb'ecomes energizedi-n-this circuit and through,

through Fig.

further ado the; subscriber at substation, 59 presses trunk key 149 whereupon. a connecits upper left-hand armature places aground on, conductor 164, which -may be traced 2'to the winding otrelay-165 in Fig. 3. r l j i 7 Relay 165 immediately cuts off connection between the substation 59and the linkciri the line leading to substation 59 will be cuit and through its outer right-hand armature places a ground on conductor129 sothat when relay 127 shortly becomes deenergized marked as busy. I p 7 Upon the energization of relay 150, relay 158 will become energized in a circuit from ground, the front contact and right-hand armature of relay 150,;windingof-relay 158, normal contacts of the inner right-hand armature of relay 158, innerright-hand armature and back contact of relay 5 toibatmy and ground Relay 158 becomes operated and looks through the alternate, contacts of its inner right-hand armature to the winding of relay 5, thereby opening the battery connection so that ;noother relay such-as 58 shown on the same horizontal line therewith may be operated.

Relay 158 through its left-hand armatures and front contacts connects the substation 59 to the trunk conductors 1 and 2; Relay" 6'? being in series therewith becomes operated and by opening the circuit of relay 65 allows this relay to become deenergized. Upon the release of relay -65, relay 66 becomes deenergized and thencein turn shortcircuits the windingfof relay 67 so that the trunk holding circuit is now returned to normal.

The subscriber at'substation' 48 now,hav-

ing delivered his message replaces his receiver i on its hook thereby causing thedeenergization of relay 99. In a short interval relay 100 becomes deenergized, followed shortly thereafter by the'release ofrelay 101. This in turn releases relay 103,-whereby ground r is removed from conductor 89 and relay 91 is allowed toreturn to normal. Relay 91 returning to-normalextends' a circuit from ground through the normal contact of its lefthand armature, brush 102 to the contact on which this brush is now resting, through the 1 back contact and armature of stepping magnet 115, winding of relay 114, winding of magnet 115 to battery and ground. Magnet 115 is now me self interrupting circu-itand will automatically step the brushes 102 and 3117 to their normal position. When ground has'been removed from conductor 89 and brushes 102 and 117 havebeen restored to normal, then the line finder relay 84;.and the connector relay 127 are released, so that the link circuit is now entirely restored to :normal. V

f At' this point it will be noted that otall the-relays which were energized duringthe establishment of the link circuit connection, 79- is the only one now remainingoperated. This is, however, due to the fmechanical l atch 193, This arrangement insures that the next -local;call' will be established through the second-link circuit, that is, the upper one .:s hown in Fig; 4 and through a similararirangemen-t thethird l1nk circuit shown in the lower apartuof F ig. 4will be the next to corresponding to relays 11 0 and 779 andthe .deenergizat-ionof relay 149- corresponding to relays 11,1 and 80, a circuit is completed from battery, winding of relay 190, outer rightture and front contact places a ground on conductor 195 leading inmultiple to the windingsot magnets 196 and 94, Magnet 196 will unlatch the armature of relay 1 1 10, and

.. 7 be used, ,Upon the energization of, relay148 magnet 94 will unlatchthe armatureot-relay 7 9 so that it eitheror bothof these link circuits h.,ave now become idle, they will-be returned to normal-condition and thescirc uit for relay 190 will be opened. It on the other hand all three link circuits are busy, then relay190will be maintained energized; in the circuit just traced and through {its righthfand armature will: place a ground on comductor 197 which maybe traced through lligs.

-'4,=3, 5and 6 to thewindingiofrelay 68.1 This -relay" through its left-handarmatureplaces aground on the winding of relay132-so-as v to start-the ringing and timing circuittrelaysinto operation. Throughits inner righthand armature relay 68 removes the a ground fronr conductor 69 "so that anyviother sub- I scriber attempting tomake a local call will find the circuit of hisl-ine relay'open; A busy {tone will be connected through the outer 7 right-hand armature and front contact of relay 132, condenser;;1-98, the outer rightha-ndarmature and front :contact of relay 68 intothe winding Offilf lllSilOIIIlQl 159 whence by induction busy tone is-transmitted through the front contact and inner-righthand armature of relay 68jancl thence over conductor 69 to the tip windings of the line relays so that the subscriber who is attempting to make a-local call Wlll'I'GCBlVGJEL busy' tone and will be notified {therebytliat all'li-n'k circuits are busy. a 1' v 7 Each link circuit is 'provided with a relay such as 76 and akey such as 170 so that should it become disabled the starter wire'may be permanently advanced to the next link circ'uit, by the operation of the key and the con-' 15, ture that when it is blown a link will complete a connection from busbar 17 2 to terminal 173 V so that battery will now be connected to conductor 1745.. Conductor 174: maybe tracedthrough Figs. 6, 5 and 3 to the normal'contact of key 170and thence to the winding of relay 76 so that this relay now becomes operated and automatically advances the starter wire. Upon the ener ization of relay 7 6 battery on conductor 17 4 is connected through the inner right-hand armature and front contact of p relay 76 of conductor 175 which may be traced through Figs. 3, 5 and 6, to the winding' of alarm relay 176. Relay 17 6 becomes energized and causes the operation of buzzer alarm 177 and signal lamp 178. Relay 176 is also connected to busbar 179 so that if any -one of the fuses 180,181 or 182 leading to other apparatus of the P. B; X. operates, a simi- 'lar alarm will be given. We-will now resume the description of the operations incident to the establishment of the connection of the central office trunk-to substation 160. The subscriber at substation 59 now hascomplete charge of the operations 1 and his telephone is connected to the trunk represented by conductors 1 and 2. The switching arrangement to the right of his trunk keys by means of which he may establish trunk connections for substation 160 is representative of other similar switching arrangementsby means of which he may establish similar trunk connections for other outlying stations. "The multiple contacts 161 and 162 lead to suchother switches. "i

The subscriber at substation 59 now operates monitoring key 163 inorder to listen in on the line of substation 160 to see if it is busy. p This connects thetwo lines together through condensers 183' and 184. Y When it is found that the line of substation 'l60is idle, key 163 is restored andkey 156 is operated for a short period. Following this key 156 is restored and key 159 is operated.

During the operation of key 156 a connec- Botion is established from source of ringing current 33 through protective resistance lamp -185,'c0nductor 186, lower alternate contacts of key 156, thence out over theline and I through the call bell of substation 160, upper alternate contacts of key 156, conductor 187 to link circuits, a second line l messes "source of-ringing current'33F In due time the subscriber at substation 1160f responds and since itEis assumed that by this time key 156 has been restored and key 159 operated the subscriber at substation 160 will be connected. 'to the trunk overthelineof substation '59.

Through contacts 188 and 1890f key 159, trunk relay'199 is energized andground is placedon conductor 212 to mark the line" of substation 160 as busy. The contacts 213 and 214 of key 159 arein multiple'with contacts 154 and 155 of substation 59. so that if new the subscriber at substation 59 is satisfied that the trunk call has been properly extended he will restore his handset to its stand and relays 150 and 158 will be maintained operated.

Should the subscriber at substation 59 wish to communicate secretly with the subscriber at substation 160 he will in, the manner hereinbefore described request the subscriber on the central office trunk to wait and then by pressing his holding key 215 will hold the trunk while he establishes an independent local connection from his substation through one of the link circuits to substation 160.

' lVhen the proper information has been passed he will then reestablish the trunkcall in the manner hereinbefore described'an'd then by manipulation of key 159 put the subscriber at station 160 in communicationfwith the sub--- scriber'calling over the central oflice line.

What is claimed is:- V 1. In a telephone system,trunk lines, link circuits; a first line-having access to said link circuits, a second line having access to both said link circuits and said trunk lines, 7

and switching means connected to said second line individual to said first line for giving said first line access to said trunk hnes.

Y 2 .'In a telephone system, trunk lines, link circuits, a first line havin access to said having access-to both sald link circuits and said trunk lines,

substations on said lines, and switching I means individual to said first, line at the substation of said second line wherebysaid'first line may be given access to said trunks over said second'line'. I l In a-telephone system, trunk lines, link circuits, a'first line having access to said'link circuits, a second line having access to both said link circuits and said trunk lines, switching means individual to said first line connectedto said second line for giving said first line access to said trunklinesand switching means for establishing a monitoring connection between said lines.

4. In a telephone system, trunk lines, link circuits, a first line having a substation, a pair of talking conductors and means for connecting to saidlink circuits, a second line iaving a substation, a pair of talking conductors, means for connecting to said link" circuits, means for connecting to said trunk lines and a signaling conductor per trunk for actuating said last means, and switching means individual to said first line actuated at the substation of said second line for con necting said first line to said trunk lines.

5. In a telephone system, a party line having a plurality of stations thereon, a trunk line accessible to said line, a holding circuit associated with said trunk line, means including a key at each of said stations for op erating said holding circuit and a relay individual to each of said stations for opening the connection to the holding key at the other of said stations.

6. In a telephone system, a party line havstations.

7 In a telephone system, a party line having a plurality of stations thereon, links and trunks accessible to said line, means under control of said stations for selectively establishing a connection from said line to one of said trunks, means under control of said stations for automatically establishing a connection from said line to one of said links, means responsive'to the establishment of a connection from said line to one of said trunks for cutting off said link connecting means, and a relay individual to each said station on said line responsive to the operation of said first means for individualizing control of said trunk and link connecting means in the station on said line first to assume such control.

8. In a telephone system, trunk lines, lin circuits, a first line having a substation and extending to switching means for connecting said first line to said-trunks and to said links, a second line havinga substation and extending from said substation to switching means at said first line substation and from thence to switching means for connecting said second line to said links only, said switching means at said first substation for extending a connection from said second line substation over said first line whereby said second line may be connected to said trunks.

In witness whereof, I hereunto subscribe my name this 12th day of March, 1929. 7

CHARLES D. KOEOHLING. 

